The demand for energy (and the hydrocarbons from which that energy is derived) is continually rising. However, hydrocarbon raw materials used to provide this energy often contain difficult-to-remove sulfur and metals. For example, sulfur can cause air pollution and can poison catalysts designed to remove hydrocarbons and nitrogen oxide from motor vehicle exhaust, necessitating the need for expensive processes used to remove the sulfur from the hydrocarbon raw materials before it is allowed to be used as a fuel. Further, metals (such as heavy metals) are often found in the hydrocarbon raw materials. These heavy metals can poison catalysts that are typically utilized to remove the sulfur from hydrocarbons. To remove these metals, further processing of the hydrocarbons is required, thereby further increasing expenses.
Currently, there is an on-going search for new energy sources in order to reduce the United States' dependence on foreign oil. It has been hypothesized that extensive reserves of shale oil, which constitutes oil retorted from oil shale minerals, will play an increasingly significant role in meeting this country's future energy needs. In the U.S., over 1 trillion barrels of usable, reserve shale oil are found in a relatively small area known as the Green River Formation located in Colorado, Utah, and Wyoming. As the price of crude oil rises, these shale oil resources become more attractive as an alternative energy source. In order to utilize this resource, specific technical issues must be solved in order to allow such shale oil reserves to be used, in a cost effective manner, as hydrocarbon fuel. One issue associated with these materials is that they contain a relatively high level of nitrogen, sulfur and metals, which must be removed in order to allow this shale oil to function properly as a hydrocarbon fuel.
Other examples of potential hydrocarbon fuels that likewise require a removal of sulfur, nitrogen, or heavy metals are bitumen (which exists in ample quantities in Alberta, Canada) and heavy oils (such as are found in Venezuela).
The high level of nitrogen, sulfur, and heavy metals in oil sources such as shale oil, bitumen and heavy oil (which may collectively or individually be referred to as “oil feedstock”) makes processing these materials difficult. Typically, these oil feedstock materials are refined to remove the sulfur, nitrogen and heavy metals through processes known as “hydro-treating” or “alkali metal desulfurization.”
Hydro-treating may be performed by treating the material with hydrogen gas at elevated temperature and an elevated pressure using catalysts such as Co—Mo/Al2O3 or Ni—Mo/Al2O3. Disadvantages of hydro-treating include over saturation of organics where double bonds between carbon atoms are lost and fouling of catalysts by heavy metals which reduces the effectiveness of hydro-treating. Additionally hydro-treating requires hydrogen, which is expensive.
Alkali metal desulfurization is a process where the oil feedstock is mixed with an alkali metal (such as sodium or lithium) and hydrogen gas. This mixture is reacted under pressure (and usually at an elevated temperature). The sulfur and nitrogen atoms are chemically bonded to carbon atoms in the oil feedstocks. At an elevated temperature and elevated pressure, the reaction forces the sulfur and nitrogen heteroatoms to be reduced by the alkali metals into ionic salts (such as Na2S, Na3N, Li2S, etc.). To prevent coking (e.g., a formation of a coal-like product) however, the reaction typically occurs in the presence of hydrogen gas. Of course, hydrogen gas is an expensive reagent.
Another downside to processes requiring hydrogen in oil feedstock upgrading is that the source of hydrogen is typically formed by reacting hydrocarbon molecules with water using a steam methane reforming process which produces carbon dioxide emissions. This production of carbon dioxide during the hydro-treating process is considered problematic by many environmentalists due to rising concern over carbon dioxide emissions and the impact such emissions may have on the environment.
An additional problem in many regions is the scarcity of water resources needed to create the hydrogen. For example, in the region of Western Colorado and Eastern Utah where parts of the Green River Formation of shale oil is located, the climate is arid and the use of water in forming hydrogen gas can be expensive.
Thus, while conventional hydro-treating or alkali metal desulfurization processes are known, they are expensive and require large capitals investments in order to obtain a functioning plant and can have adverse environmental effects. There is a need in the industry for a new process that may be used to remove heteroatoms such as sulfur and nitrogen from oil feedstocks, but that is less expensive and more environmentally friendly than conventional processing methods.
U.S. patent application Ser. No. 12/916,984 provides an approach for removing sulfur and nitrogen heteroatoms (and heavy metals) from shale oil, bitumen, and heavy oil by using a hydrocarbon material, such as methane, in connection with sodium metal. (This prior patent application is published as U.S. Patent Application Publication No. 2011/0100874 and is referred to herein as the “'874 application.”) The present disclosure builds upon and modifies the approach of the '874 application. Accordingly, it is presumed that the reader is familiar with the teachings of the '874 application